A box from 0 to 1 of height 1. What is its median ?

Interpretation/Attempt: A random variable, X, is uniform, (So that its density is f(x)=1for0≤x≤1.), but how do I find the mean ?

-Part b)

Consider the following random variable and probability mass function:

X = {2,3,4,5}

P(X =2)=0.1, P(X =3)=0.2, P(X =4)=0.3 P(X =5)=0.4

What is the variance of X?

I have the lecture notes for this but that's all I can relate.